Radio shielded spark plug



Jam 9, 1940- M. F. PETERS ETAL RADIO SHIELDED SPARK PLUG Filed Aug. 2l,1935 5 Sheets-Sheet l I INVENToRs M F. Peters and (W. Asrn Figa ATTORNEYJan. 9, 1940. M PE1-ERS ET AL 2,186,039

RADIO SHIELDED SPARK PLUG Filed Aupa, 1935 s sheets-sheet 2 al L@ if? @d3 S8 gg/ sa F q 7 mvENToRs M.F. PeTer-s and AV. AsTn BY ATTORNEY M. F.PETERS ET' AL RADIO SHIELDED SPARK PLUG Jgn. 9, 1940.

Filed Aug. 2l, 1935 5 Sheets-Sheet 3 mvENToRs M. F. Peters and A.V.AsnBY F913 www Figla Jan. 9, 1940.

M. F. PETERS ET AL 2,186,039

RADIO SHIELDED SPARK PLUG Filed Aug. 21, 1935 5 Sheets-Sheet 4 ylNvEN-ToRs M. F.`Pefers' and AV. Ashn ATTORNEY Jan. 9, 1940. M. F.PETERS I-:r AL 2,186,039

RADIO SHIELDED SPARK PLUG Filed Aug. 21, 1935 5 Sheets-Sheet 5 VARIATIONOF NOISE WITH SIZE OF OPENING IN PLUG- sHIELDING. (COMPLETELY OPENREADING Iso) i NOISE READING n ou I 2 RATIO OF SLOT WIDTH T0 STRIP WIDTHFIB. 20 5 I I L I L. NoIsE VARIATION WITH NUMBER E 3 oI= oPENINGs TOTALwIoTI-I 0F 5 oPENING= TOTAL wInTI-I oF I cLosING STRIP Ld 0 2 I I l l I5 G I 1 NUMBER OF OPENINGS .aI MEIQIIIIEIIIRVMI BY y ATTORNEY PatentedJan. 9, 1940 UNITED STATES vPATENT OFFICE Melville F. Peters and AllenV. Astin, Washington, D. C.

Application August 21, 1935, Serial No. 37,176

27 Claims.

(Cl. 12S-169) (Granted under the act of March 3, 1883, as

amended April 30,

This invention relates to spark plugs and particularly to spark plugswhich are provided with a shielding to reduce or eliminate thedisturbance that their operation produces on nearby radio receivingsets.

Among the objects of this invention are: To provide an adequately radioshielded spark plug; to provide a shielded spark plug with aircirculation around the upper assembly of the plug; to provide a shieldedspark plug that reduces the heating of the high tension ignition cableconnected to the plug; to provide a shielded spark plug of reduced sizeand weight; to provide a spark plug in which the upper terminal andcontacts are hermetically sealed; to provide a spark plug which uses anew type of fin, where the ns serve for radio shielding, to provide aspark plug which cools the ignition harness, to provide cooling of shellelectrodes, thus increasing the life; to provide a radio shielded plugin which the danger of flash-over due to accumulation of dirt andmoisture is reduced; to provide a radio shielded plug of highanti-preignition properties without increasing fouling tendencies.

In the drawings:

Fig. l is a longitudinal section of a shielded spark plug embodying ourinvention;

Fig, 2 is a side elevation thereof on a reduced scale;

Fig. 3 is a longitudinal section of an element for connecting the shieldof the plug to the shieldingT harness of the cable: l

Fig. 4 is a longitudinal section of a spark plug embodying theprinciples of our invention in a somewhat different structural form;

Fig. 5 is a partial longitudinal section of a spark plug wherein theprincipal part of spark plug shield is continuous but is connected tothe spark rlug base 'by a. plurality of short bars;

Fig. 6 is an element for the same purpose as that in Fig. 3 but havingdifferent structural form:

Fig. '7 is a longitudinal section cf acenter electrode of a spark plugpartly adapted for use with our novel shielding;

Fg. 8 is a View, partially in longitudinal secii'vn, of a still dilerentembodiment of the principles of the present invention;

il is. an inverse sectional View of one form of spark plug shieldingmember;

Fig. lil is top plan view of the element which connects the spark plugshield in Fig. 8 to the cable shielding harness;

Fig. 11 is a longitudinal sectional view illustrating the use of a heatradiating and air bailling member in connection with a spark plugshield;

Figs.- l2 and 13 illustrate two means of mounting a connecting elementon a circumferentially corrugated flexible tube to decrease the lengthof the means for connecting the spark plug shield to the shield harnessproper.

Figs. 14 and l5 are respectively a transverse section and a fragmentaryelevation partly in section, of the shield shown in Fig. 1 modified byproviding it with wrench lugs;

Fig. 16 illustrates a spark plug shield provided4 with circumferentialfins to augment the heat radiating properties of the shield;

Fig. 1'7 discloses a shield having the longitudinally extending barstransversely corrugated to increase the length of the path of heattransfer between the ends of the shield;

Figs. 18 and 19 are respectively a plan View and n Fig. 2l shows therelation between noise and o the number of openings in the spark plugshield, where the total width of opening is equal to the total Width ofthe strips connecting the ends of the spark plug shield.

The manner in which the above objects are obtained by our invention willbe better understood after consideration of the theory involved in theshielding of spark plugs.

An ignition system for automotive engines comprises a high tensioninsulated wire connecting a source of ,current at high potential to theinsulated center electrode of a spark plug. As increasing voltage isapplied to the plug, the gap breaks down and the current passes acrossthe gap between the spark plug points and returns to the source by apath that includes the engine. If the high tension portion of thecircuit is surrounded by a metal casing, the greater portion of thecurrent, after passing through the spark gap, returns through the metalcasing or shielding harness. A portion of the electro-magnetic l'ieldset up between current in the high tension part of the circuit isneutralized by the electro-magnetic field of the current flowing in thehigh tension portion of the circuit. The flow of the major portion ofreturn current through the shielding harness is due to the fact thatthis tends to make the total or resultant magneti; field a minimum. Thisis known as the proximity effect. I any portion of the shield circuitdoes not completely surround the adjacent portion of the high tensioncircuit, the electro-magnetic eld produced by the current flowing in thehigh tension ignition cable will be distorted by the current returningthrough the partly surrounding shield so as to vtend to produceneutralizatiton of the radiating elds.

The shielding harness surrounding the ignition cable is long incomparison with the shielding around the spark plug. If the shieldingaround the spark plug is removed, but means are provided for lthecurrent to return through the shield around the cable, the shieldingwill be effective. Furthermore, ifthe path provided for the returncurrent from the spark plug shield to the cable shielding'harness isplaced near the shank of the spark plug, the two fields will bedisplaced to make the resultant eld a minimum.

In view of the foregoing, one of the important aspects of the presentinvention consists in providing a connection between the shell of thespark plug and the cable shielding harness in which the path in thisportion of the return circuit is near and parallel to but insulated fromthe core of the spark plug and in which the average radial angle at thecore subtended by the metal of the path is greaterthan zero degrees andless than 360 degrees.

The relative effectiveness of the described method of suppressing radiointerference depends in the general case upon the ratio of the totalangle subtended by the conducting strip (or strips) at the axis of thecenter electrode to the total angle subtended by the openings. Therelative effectiveness of the interference suppression depends furtheron the distribution of the conducting strips around the centerelectrode. For any given arrangement of the strips there is littlechange in the effectiveness of shielding as long as the ratio of theangle subtended by the strips to the angle subtended by the openings isequal to or greater than one. Cooling of the plug and cable increases asthe openings are increased so from this point of view it is desirable tohave the openings as large as possible. An optimum value, from bothpoints of view, would be to have the openings approximately equal to thestrips. The effectiveness of the suppression of noise increases, for anygiven total angle subtended by the strips, as the number of stripsincreases. The greatest changes are from one to two and two to three. Asthe number of strips is increased beyond three the change in shieldingeffectiveness is much more gradual and beyond Vsix is almost negligible.Since the cost of plug manufacture is likely to increase as the numberof strips is increased it does not seem worth while to increase thenumber of strips to much beyond six.

Tn certain special arrangements of ignition systems the gains inshielding effectiveness byl distributing the .conducting strips aroundthe center electrode and decreasing the size of the opening as comparedto strips may be quite negligible. This is true in systems where thebonds between the engine and the cable shield are critically adjusted orwhere a large mass of metal (Cowling, etc.) effectively screens theantenna ofV radio set from the plugs. In nsuch cases a two strip shieldwith openings 2 or, 3times the width of the strips provides adequateshielding.

This present invention has several features in common with the copendingapplication of M. F.'

. Peters, Ser. No. '756,43l, led Dec.. '7, 1934.

Referring toFig. l, I4 designates a sparklplug shell to which are fixedsparking points I having in them a'core I6 of copper to increase theheat conducting properties of the points and so reduce the ,rate of wearof the points due to high temperature. Engaged with shell I4 is a glandnut I1 within which is a bushing I8,of metal preferably of high thermalconductivity. The center electrode I9 comprises a shank 2D carryingsparking terminal 2| disposed between the points I5, the shank 20 beingof reduced cross sectional area from the nose of the electrode to apoint adjacent to the outer face of clamp nut I'I and around thisreduced portion is disposed a sheath ZIa of metal having high thermalconductivity. Insulating material 22, which may be mica washers, is heldin position betwen the nose of the center electrode and bushing I8. Thecenter electrode I9 has in it an axial bore 23 from its outer end to apoint adjacent the outer end oi sheath 2 Ia and in the outer portion ofthe base is a plug 24 which is one means of preventing collapse of thehollow tube when assembling. The plug 24 is not necessary and undercertain conditions may be left out to advantage. Other methods ofassembly do not require it. The terms outer and inner as used hereinrefer to the relative positionsof the parts with respect to thecombustion chamber of an engine in which the plugs will be used. A micacigarette 24 is disposed around sheath 2Ia and the outer portion ofcenter electrode I 9 to a point adjacent the inner end of filling 24 andmica washers 25 are disposed around .the cigarette between the outerface of nut I'I and externally threaded member 25 of good thermalconductivity that is secured to the outer end of center electrode I9.

The radio shielding' for the spark plug proper comprises a plurality oflongitudinally extending bars 2B which are preferably separated fromeach other by spaces having substantially the same width as the barsthemselves. These bars may be formed integrally with the spark plugshell I4 or they may be secured thereto in any suitable manner such asby welding, brazing, threading or screws. The number of barsused dependssomewhat upon the particular conditions of operation to which the sparkplug will be subjected, the length of leads and position and method ofbonding, the essential feature being that spaces are left open throughthe shielding around the spark plug to permit of air circulation todissipate heat from the outer assembly of the spark plug. The bars alsoserve as iins for 'cooling the core of the plug. While our shield isshown made with longitudinal bars it is satisfactory in many cases touse a continuous tubular member 21 Fig. 5) connected to the base of thespark plug by bars 28 or the spark plug shield may be of conventionalform with more or less irregularly distributed apertures formed therein.

The copper cores I6 in spark points I5 conduct heat rapidly from theextremities of the points to shell I4, whence, it is conducted outwardlythrough the shell into the engine and to the bars 26; yalso the highconducting sheath 2Ia rapidly transfers heat from the nose of centerelectrode I9 to the bushing I8 and thence to clamp nut I'I and shell I4.The shank 20 is bored to diminish the cross sectional area in the upperassembly as shown at 23, which reduces the thermal conductivity of theelectrode and thus lessens the quantity'of heat carried to the topterminal and minimizes cable burning, thus decreasing the thermalexpansion of the shank in the upper coreassembly. However, the heat thatis transmitted along the electrode and the mica. Washers in the uppercore'assembly' to the tube terminal 26 is conducted through theinsulator 32 which in turn is cooled by the circulation of air. The heatis, therefore, dissipated before reaching the cable.

The bars 26 may bev made of materials having low thermal conductivitiesor high thermal conductivities or of different materials in differentportions of their length; that is, the inner onethird ory innerone-half, or other fractions of the length of each bar may be made of apoor conductor, examples of which are stainless steel or nickel-chromealloy and the remainder of each bar be made of copper or aluminum orother good conductor of heat. Or in some cases, the inner portion may beof a good thermal conductor and the outer portion of a poor thermalconductor, the relative positions of the two materials of differentthermal conductivity being determined by the flow of heat in theparticular service for which the shielded plug is to be used, or the Ibars may be made of poor thermal conductivity materials and metalsplated on the base to produce any desired thermal conductivity.

The mica washers or other insulation used in lieu thereof are formedwith a shoulder 29 upon which is seated a sealing gasket 30 againstwhich is disposed shoulder 3| of insulating sleeve 32. A nut 33 of goodthermal conducting material is disposed within sleeve 32 and engagedwith the threads on member 25. the nut 33 having longitudinallyextending flanges 34 at its ends to provide a large heat transfersurface in contact with sleeve 32 to insure efficient transmission ofheat from the outer end of the center electrode through the sleeve 32.All edges 33 and 34 may be rounded to prevent large electrical gradientsin the insulation and around the spring, which prevents formation ofozone. A tubular member 35 of insulating material is disposed in theouter end of sleeve 32 and extends somewhat beyond the outer end of thesleeve, the inner end of the member 35 resting upon electrical contactmeans which, in the instance shown. comprise a metal disc 36 adapted tobe contacted by the ignition cable and a spring 31.

Connected to the outer end of the spark plug shield is an electricallyconducting member 38 provided with threads to engage a securing element39 whereby the member 40 through which the ignition cable passes andwhich forms the intermediate connection between the spark plug shieldand the cable shielding harness is secured to the spark plug shield. Asealing gasket 4| is held under compression by a flange 42 on the memberand thus by means of the gasket 4| and the gasket 30 the outer end ofthe center electrode is effectively protected against access of moistureand dirt. The member 40 may be of stainless steel to provide a path ofhigh resistance to heat transfer or it may be of relatively high thermalconductivity depending upon the flow of heat when in use. At the presenttime, practice recommends it be given a large cross section area and bemade of a good conductor of heat. It should be chromium plated, forprotection against chemical reaction due to its surroundings, or cadmiumplated or otherwise.

The spark plug shield above described eliminates one great objection topreviously known shields lin that the free circulation of the airtherethrough carries away any particles of gas. liquid, o solid matterthat be forced through the spark plug by the pressure in the enginecylinder. Hence. the plug does not become dirty and thereby acquire astrong tendency to loss of current and flash-over. While a singleconnection between the shell of the spark plug and the shielding harnessof the cable will in most cases prevent any observable interference withradio, a stronger shield and more satisfactory service un 'der allconditions is attained when a plurality of the symmetrically spaced bars26 are used.

Fig. 9 shows a modification of the arrangement of bars 26 wherein thecorresponding bars 26 are so turned that the major faces thereof lie atan acute angle to a radius of the shield instead of the said major facesdefining substantially cylindrical surfaces. The bars in this positiondeflect the air into the shield and cause more rapid flow of air overthe spark plug itself.

In Fig. 4 the parts corresponding to the elements previously describedin Fig. 1 are designated by the same reference characters. However, inthis figure the bore 45 in center electrode i9 extends throughout thelength of the shank of the electrode and instead of having an externalsheath of material having high thermal conductivity the inner part ofthe bore contains a filling 46, of material such as copper, silver,aluminum, or other metal having high thermal conductivity, to a pointadjacent the outer face of the nut The insulating material 48 extendingfrom nut |1 to the outer extremity of electrode |9, which material isshown as composed of mica washers, has embedded in it an outwardlyfacing metallic cup 49 that ts closely the mica cigarette 24. Seatedupon a sealing gasket 50 in the cup 49 is one end of the hollow element5| which serves to connect the spark plug shield 52 with the cableshielding harness. The element 5| has in it insulating material 53 whichis shaped to receive and fit closely the insulating material 48outwardly of cup 49 and also has in it a recess 54 to receive theignition cable.

Connection between electrode I9' and a cable in recess 54 is effected bya screw 55 which may be turned to penetrate the cable and secure itfirmly in the element 5|, the screw being in contact with a cup 56 whichembraces and contacts cap 51 secured to electrode I9'. A coupling 56 ofthe well known union type may be used to secure the element 5| inoperative relation with the plug shield 52. The bars 26 of shield 52 maybe of metals of different thermal ccnductivities as above described, andlikewise the metallic element 5| may be of either low or high thermalconductivity depending uponheat flow conditions. In all this discussionit is the factor KA which is important where K is the average thermalconductivity of the cross sectional area A. Whether the good conductoris placed inside or Aoutside the poor conductor is unimportant.

In Fig. 8 Aa grid-like skeleton 59 of material such a steel is securedto shell I4 of the plug and the plug shield 6U of softer metal isdie-cast to embed the skeleton 59 therein. The shield 69 may or may notconsist of longitudinal bars, access of air thereto being affordedthrough the member 6| mounted on the outer end thereof, which member isprovided with openings 62 as as shown in Fig, 10. The member 6| has acylindrical portion 63 that lies co-axially with the center electrode ofthe spark plug and extends sorne distance into the plug shield 6U. Aninsulating sleeve 64 disposed in the cylindrical portion of member 5|has threaded engagement with the insulation 65 around the outer portionof the center electrode which thus protects from moisture and dirt theconducting eements connected to that electrode. Secured to the member 6|is a 15 flexible member 66 for connecting the plug shield to the cableharness. As is shown in the drawings, the member 66 is made ofcircumferentially corrugated flexible metal tubing, which is readilybent to adapt the position of the outer connecting member 81 carriedthereby for connection to the harness. Member 68 may be made moreconductive of heat by plating it with copper, which may be protectedfrom attack by flashing it with chromium. An effective seal is obtainedby means of the gasket 88 clamped by the flange 69 secured to the member66 and the outer faces of sleeve 84 and member 6|. between the centerelectrode and the cable is effected through disk |00, stem and spring|02. Metal bosses |03 on metal sleeve or strips |04 carry heat from stem|0| and transfer it through insulating sleeve 64 to cylindrical portion63 and so reduce the heat imparted, by conduction, to the cable.

It has been found that for use on some engines the method of connectingthe flexible tubing B6 to the spark plug shield and the harness asdisclosed in Fig. 8 requires more room than is available and, therefore,we have devised the means shown in Figs. 12 and 13 for associating acoupling member with the flexible tubing 66. This consists in securingangular washers 1| to a radially extending face of a corrugation andwhen so constructed the length of the assembly is very materiallydecreased.

Fig. 3 shows a connecting element adapted for use with a. known type ofspark plug shield and cable harness. The exterior metal member 'l2 issubstantially L-shaped and has in it insulating material 13 wherein arebores 14 and 15 substantially co-axial with the two limbs of theelement. In the base of bore| 14 is a metal cup 16 which is inelectrically conducting relation with a spring 11 and a metal disc 18 atthe other end of"sp'ring 11. Insulating sleeve 19 extends into bore 14and the opening through sleeve 19 is outwardly tapered at 80 to receivea frusto-conical member 8| with which is engaged a rubber gasket 82.When the ignition cable is inserted into sleeve A19 to contact the disc18 and the harness around such cable is connected to the element 12 therubber gasket 82 is brought into sealing contact with the end of 12.'I'he insulation in the other limb of element 12 extends beyond theouter metal portion and when in operative assembly is received in theVspark plug shield. A metal member 83 is secured against the end of theprotruding insulation 84 by the pin 85 that has screw threadedengagement with the insulation as shown at 86. Coupling element 81effects operative engagement with the spark plug shield and pressesgasket 88 into sealing relation with the end of such shield. The pin 85is preferably made of stainless steel or other poor thermal conductorand while serving as an effective connecting element between the centerelectrode of the plug and metal cup 16 it reduces. the transfer of heatto the cup 16. The limb of element 12 that surrounds pin 85 is also ofpoor thermal conducting metal while that part of element 12 around theother limb is a good conductor of heat whereby the transmission of heatto the shielding around the cable is largely prevented and such heatasdoes reach that portion of the shielding is rapidly conducted away and Ydissipated. Or the conductivity of the limbs may be reversed or madeboth good conductorvor both poor conductor.

The Fig. 6 is an alternative embodiment of our Electrical connectioninvention which may be used in the same manner as that shown in Fig. 3but is simpler to manufacture. metal member 98 is recessed at 9| toreceive the ignition cable and in the bottom of this recess is a spring92 in contact with a metal cup 93 connected to a wire 94 that has 10Wthermal conductivity and is adapted to contact the center electrode of aspark plug through the exposed screw head 95 on the end of theprotruding insulation at 96.

An additional heat dissipating element for use with a shield of the typeshown in Fig. 1 is illustrated in Fig. 11. A disc 91 of metal that is a.good conductor of heat is clamped between the member 38 and the sparkplug shield having bars 26, the lower face of disc 91 is polished toreflect radiant heat and the upper face thereof is blackened to make itan eicient radiator of the heat received by conduction from the parts ofthe shielding equipment. This disc further serves as a deector of heatwhere rising from the parts below it and so tends to prevent heating ofthe cable harness by such currents of air. All parts of the spark plugmay be made black to increase radiation or polished to reflect radiationdepending upon the surroundings.

As heretofore pointed out one of the features of the present inventionis the attaining of efficient heat radiation, conduction and convectionfrom the spark plug in engine operation under maximum loads with theradio shielding and one of the important features by which-this resultis secured is providing the center electrode of the spark plug with aportion that is a good conductor of heat from the nose of the centerelectrode to the exposed portions of the shell and clamp nut, which goodconductor is shown in Fig. 1 as an external sheath a of metal having ahigh thermal conductivity. To prevent buckling of the sheath 2|a due tounequal increase in length of the sheath 2|a and the center electrode I9we provide a gap as indicated at 98 in Fig. '7 to allow the sheath 2 |afreedom of expansion without abutting the adjacent shoulder on .theelectrode shank. The gap may be of the order of im of an inch.

The form of our invention shown in Fig. 1 is screwed into the engineblock by engaging suitable lugs on a wrench in the slots between thebars 26, but when those bars are either partially or wholly of one ofthe softer metals they may be distorted, and we may therefore providethe lugs |00 on the base of the plug, as shown in Figs. 14 and 15, to beengaged by the wrench.

When indicated as desirable by a study of heat fiow conditions inanycase. we may increase the radiation from the plug shield by addingcircumferential ns |6| (Fig. 16) to the top of the shield. flns |02 tothe bottom thereof. or both. The above mentioncdflns are preferably madeof metal having high thermal conductivity and plated with chromium or.the like to prevent chemical Acorrosion thereof.

Heat flow from the base of the spark plug to the high tension cable maybe greatly retarded by lengthening the path traversed between thosepoints by means of transverse corrugations |03 in the strips 26' asdisclosed in.. Fig. 17. This is effected not only by the increase indistance froml base to cable but also by the augmented radiation fromthe greater surficial area of the strips. It is to be vunderstood thatthe metal used in the strips 28' will be varied to suit thermalconditions during operation, as heretofore explained.

The insulating material 89 in The quantity of heat conducted through thespark plug shield from the plug base to the cable is further limited bysubstituting the connecting nipple 38 shown in Figs. 18 and 19 for thenipple 38 in Fig. l. The nipple 38 is solid throughout its length,whereas the threaded end portions IM and are separated except for theconnecting bars |06. It is obvious that the latter form not only offersmuch greater resistance to the ilow of heat from one end to the otherthan does the former, but also it improves the air circulation throughthe spark plug shield.

Figs. and 21 give in graphic form the results of measurements on thevariation of the effectiveness of shielding with changes in the ratio ofslot width to strip width, and in the number of slots. respectively.

In Fig. 20 the ordinates represent the noise `(expressed in arbitraryunits) from an ignition system and the abscissae represent the ratio ofthe total width of the slots between the bars-or strips to the totalwidth of the bars themselves. The numbers adjacent the several curvesindicate the number of the connecting bars 'of the shield upon which themeasurements were made for each curve. The curves IA and 2A representresults obtained when the bars were somewhat farther from the spark plugcorethan were the bars in the other cases in this figure. In all casesinvolving a plurality of bars, the bars were symmetrically disposedaround the core, which arrangement has been found to give a minimum ofnoise for any size or number of bars. It will be observed that the noiseincreases with increase of ratio between Width of slots to width of barsand with decrease in the number of bars, but that no practical benefitsare obtained by using more than six bars when the ratio of slot width tobar width is one or less.

Fig. 21 demonstrates that twelve bars, when total slot width equalstotal strip width, give as effective shielding as does a completeinclosure of the plug in an electrically conductive shield, and inaddition there is derived the benet of cooling and the prevention offouling as above set forth. This figure shows also that from thestandpoint of commercial production six bars and slots of equal totalwidth are probably most desirable.

The data in the curves were taken with the pick-up antenna of the noiseindicator one foot from the high tension cable. 'I'he relativedifferences between any observation and that for the completely inclosedplug decrease as the -antenna 'is moved to a greater distance from thecable and metallic objects are interposed between the antenna and thespark plug, so that considerable practical shielding is obtained when a.single small bar connects the base of the plug to the cable shield.

The invention described herein may be manufactured and used by o r forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

We claim:

1. In combination, a spark plug including a shell and a center electrodehaving in it an axial bore extending from its outer end to a pointadjacent its inner end and a filling of material of high thermalconductivity in said bore extending from the inner end of said bore overa distance between one-fourth and one-half of the length of said bore,insulating material around said inner electrodev extending inwardly fromthe outer end of said electrode over a substantial por- Y tion of itslength, an outwardly facing cup embedded in said insulating material, ametal cage mounted on said shell and surrounding the outer portion ofsaid plug, said cage including longitudinally extending bars separatedfrom each other by spaces substantially equal in width to the width ofthe bars, the said bars being made of material of high thermalconductivity for substantially one-half their length and of material oflow thermal conductivity for the remainder of the length thereof, andmeans for electrically connecting the shielding harness of an ignitioncable to said cage and a cable to said inner electrode, said meanshaving a portion seated in said cup. A

2. In combination, a spark plug including a. shell and a centerelectrode having in it an axial bore extending from its outer end to apoint adjacent its inner end and a filling of material of high thermalconductivity in said bore extending from the inner end of said bore overa distance between one-fourth and one-half of the length of said bore,insulating material around said inner elect-rode extending inwardly fromthe outer end of said electrode over a substantial portion of itslength, an outwardly facing cup embedded in said insulating material, ametal cage mounted on said shell and surrounding the outer portion ofsaid plug, said cage including longitudinally extending bars separatedfrom each other by spaces substantially equal in width to the width ofthe bars, the said bars being made of material of high thermalconductivity for substantially the inner half of their length and ofmaterial of low thermal conductivity for the remainder of their length,and means for electrically connecting the shielding harness of anignition cable to said cageand a cable to said inner electrode, saidmeans having a portion seated in said cup.

3. In combination, a spark plug including a shell and a center electrodehaving in it an axial bore extending from itsI Aouter end to a pointadjacent its' inner end and a lling of material of high thermalconductivity in said bore extending,

from the inner end of said bore over a distancef between one-fourth andone-half of the length of said bore, insulating material around saidinner electrode extending inwardly from the outer end of said electrodeover a substantial portion of its length, an outwardly facing cupembedded in said insulating material, a metal cage mounted on said shelland surrounding the outer portion of said plug, said cage includinglongitudinally extending bars separated from each other by spacessubstantially equal in width to the width of the bars, the said barsbeing made of material of thermal conductivity for substantiallytheouter half of their length and of material of low thermalconductivity for the remainder of their length, and means forelectrically connecting the shielding harness of a cable to said cageand a cable to said inner electrode, said means having a portion seatedin said cup.

4. In combination, a spark plug including a shell and a center electrodehaving in it an axial bore extending from its outer end to a pointadjacent its inner end and a filling of material of high thermalconductivity in said bore extending from the inner end of said bore overa distance between one-fourth and one-half of the length of said bore,insulating material around said inner electrode extending inwardly fromthe outer end of said electrode over a substantial 75 i portion oi itslength, an outwardly facing cup embedded in said insulating material, ametal cage mounted on said shell andsurrounding the outer portion ofsaid plug, said eige including longitudinally extending bars separatedfrom each other by spaces substantially equal in width to the width ofthe bars, and means for electrically connecting the shielding harness ofa cable to said cage and a cable to said inner electrode, said meanshaving a portion seated in said cup.

5. In combination, a spark plug including a shell and a center electrodehaving .in it an axial bore extending from its outer end to a pointadjacent its inner end and a filling of material of high thermalconductivity in said bore extending from the inner end of said bore overa distance between one-fourth and one-half of the length of said bore,insulating material around said inner electrode extending inwardly fromthe outer end of said electrode over a substantial portion of itslength, a metal cage mounted on said shell and surrounding the outerportion of said plug, said cage including longitudinally extending barsseparated from each other by spaces substantially equal in width to thewidth of the bars, the said bars being made of material of high thermalconductivity for substantially one-half their length and of material oflow thermal conductivity for .the remainder of the length thereof, andmeans for electrically connecting the shielding harness of an ignitioncable to said cage and a cable to said inner electrode.

6. A shield for spark plugs, comprising a metal member disposable aroundthe outer portion of the plug having a plurality of spaced apartlongitudinally extending bars, the width of any one of said bars notexceeding the diameter of said outer portion, said member being adaptedto have electrical connection with the grounded shell of a spark plugand with the shielding harness of an ignition cable connected to saidplug.

'l'. A shield for spark plugs, comprising a metal member havinglongitudinally extending bars oi less Width than the diameter of a sparkplug separated from each other by spaces equal in width to the width ofthe bars, said member being adapted to have electrical connection withthe grounded shell of a spark plug and with the shielding harness of anignition cable connected to said plug.

8. A shield for spark plugs, comprising a metal member havinglongitudinally extending bars separated from each other by spaces equalin width to the width of the bars, said member being adapted to haveelectrical connection with the grounded shell of a spark plug and withthe shielding harness of an ignition cable connected to said plug, saidbars being made` of material having low thermal conductivity forsubstantially one-half their length and of a diierent material havinghigh thermal conductivity for the remainder-of their length.

9. A shield for spark plugs, comprising a. metal member disposablearound the outer portion of the plug, said member having a portionelectrically connectible to the grounded shell of a spark plug, aportion electrically connectible to the shielding harness of anignitioncable, and an intervening portion in which apertures are formed, saidmember being made of material having thermal conductivity of the orderof the thermal conductivity of stainless steel for at least a portion ofits length.

10. 'Ihe combination with a spark plug having a shell, a centerelectrode carried thereby and insulating material around the outerportion of said electrode, of a member partially embedded in saidinsulating material and extending outwardly beyond the outer surface ofsaid material, a laterally apertured shielding member disposed aroundthe outer portion of the spark plug in electrical connection .with saidshell, an electrically conducting sleeve extending into said yshieldingmember to seat against said partially embedded member, meansmechanically and electrically connecting said sleeve to said shieldingmember, insulating material in said sleeve extending throughout thelength of said sleeve and having in it ,spaces to receive the outer endof the spark plug and to receive a cable, and means to connectelectrically a cable in said insulating material to said centerelectrode.

1l. The combination with a spark plug having a shell, a center electrodecarried thereby and insulating material around the outer portion of saidelectrode, of a member partially embedded in said insulating materialand extending outwardly beyond the outer surface of saidmaterial, alaterally apertured shielding member disposed around the outer portionof the spark plug in electrical connection with said shell, anelectrically conducting sleeve extending into said, shielding member toseat against said partially embedded member, means to hold said sleevein electrical contact with said shielding member,

insulating material in said sleeve extending throughout the length ofsaid sleeve and having in it spaces to receive the outer end of thespark plug and to receive a cable, and means to connect electrically acable in said insulating mater rial to said center electrode.

12. In combination, a spark plug having a shell, a center electrodehollow except at its inner end and insulating material around the outerportion of the said electrode, a filling of material in the hollow ofsaid electrode, said filling having high thermal conductivity andextending from the inner-end of the hollow to substantially the innerlimit of said insulating material, an electrically shielding memberdisposed around the outer portion of said plug, the wall of said memberbeing apertured to permit the dissipation of heat from the spark plugstructure and the material over at least a portion of the length of saidmember being of low thermalconductivity, an electrically conductingsleeve connected to said member in electrically conducting relationtherewith, insulating `material in said sleeve having in it a cavity tot around the outer portion of said insulating material and a cavity toreceive a cable, and means to form electrical connection between saidcenter electrode and a cable in said last mentioned cavity.

13, In combination, a spark plug including a shell and a centerelectrode mounted therein, the inner portion of said electrode being of.high thermal conductivity as compared with the outer portion thereof,and an electrically shielding member disposed around the outer portionof said plug in electrically conducting relation with said shell, saidmember having apertures through the wall thereof. f

said shell, said member having between its ends a portion includinglongitudinally extending bars separated by spaces, the radially innerand radially outer faces of-each individual bar being set at an acuteangle to a line from the center of said electrode to said individualbar.

l5. An electrically shielding member for the outer portion of a sparkplug, comprising a hollow member having end portions and an intermediateportion including longitudinally extending bars separated by spaces, thesaid bars each having a. pair of substantially parallel faces set at anacute angle to a perpendicular from the longitudinal axis of said memberto such faces.

16.I In combination, a spark plug including a center electrode andinsulating material around the outer portion thereof, an outwardlyfacing cup member carried by and extending laterally beyond saidinsulating material, a metallic sleeve member having an end seated insaid cup member, insulating material in said sleeve having therein acavity to fit on said insulating material, and means to form anelectrical connection between said electrode and a cable extending intosaid sleeve.

17. In combination, a spark plug including a center electrode andinsulating material around the outerv portion thereof, an outwardlyfacing cup member carried by and extending laterally beyond saidinsulatingmaterial, a metallic sleeve member having an end seated insaid cup member, insulating material in said sleeve having therein acavity to fit on said insulating material, means to form an electricalconnection between said electrode and a cable extending into saidsleeve, and means to ground said sleeve'fV 18. A shielding device for aspark plug, comprising a body member disposable around the outer portionof a spark plug in electrical connection with a grounded member of theplug, and an outer member securable to the outer portion of the saidbody member, said outer member having a portion to lit in the outer endof said body member and a cylindrical portion of less diameter than thesaid body member connected to the first mentioned portion by aperforated portion, the said outer member being of material having lowthermal conductivity.

19. A shielding device for a spark plug, comprising a body memberdisposable varound the outer portion of a spark plug in electricalconnection with a grounded member of the plug, and an outer membersecurable to the outer portion of the said body member, said outermember having a portion to t in the outer end of said body member and acylindrical portion of less diameter than the said body member connectedto the rst mentioned portion by a perforated portion.

20. The combination with a spark plug having a shell and a centerelectrode, of a skeleton of rigid material carried by said shell and ashielding member of material softer than that in said skeleton disposedaround the said plug outwardly of said shell with said skeleton embeddedin said softer material.

21. The combination with a spark plug having a shell and a centerelectrode with insulating material around said electrode outwardly ofsaid shell, the outer end of said material having external screwthreads, of a shielding member disposed around said plug outwardly ofsaid shell and in electrically conducting relation therewith, an elementhaving a cup-shaped portion intertting With and seated against the outerend of said member and a cylindrical portion coaxial with saidelectrode, an insulating sleeve in said cylindrical portion engaged withthe threads on said insulating material, and means to conduct heat fromthe outer end of said electrode to said cylindrical portion through saidsleeve.

22. The combination with a spark plug having a shell and a centerelectrode with insulating material around said electrode outwardly ofsaid shell, the o-uter end of said material having external screwthreads, of a shielding member disposed around said plug outwardly ofsaid shell and in electrically conducting relation therewith, an elementhaving a cup-shaped portion interiitting with and seated against theouter end of said member and a cylindrical portion coaxial vwith saidelectrode, and an insulating sleeve in said cylindrical portion engagedwith the threads on said insulating material.

23. In combination, a spark plug shell, a gland nut internally engagedwith said shell, a bushing of material having good thermal conductivityin said nut, an insulating cigarette disposed in said bushing, a centerelectrode mounted in said cigarette, a portion of said electrodeextending inwardly from the outer end of said nut being of greaterthermal conductivity than a portion next outwardly thereof, insulatingmaterial around said center electrode substantially coterminous withsaid portion next outwardly of said nut, said material being providedwith an outwardly facing shoulder, means associated with the outer endof said electrode to increase the thermal conductivity thereof, anexternally threaded member having good thermal conductivity disposedaround and secured to the outer end of said electrode, a sleeve ofinsulating material cooperating with the shoulder on said insulatingmaterial around the center electrode to form a 4seal at that point andextending outwardly beyond the end of said electrode, an heat conductingelement engaged with the externally threaded member and in heattransferring relation with said sleeve, a cylindrical element disposedin said sleeve and extending beyond the outer end thereof, a sealingelement around said cylindrical element in contact with the outer end ofsaid sleeveradio-shielding means disposed around the outer end of saidelectrode, an element of a shielding harness for an ignition cable, andmeans to secure said last named element in cooperative relation withsaid radio-shielding means and to maintain an eiectiveseal at saidsealing element and at the'slioulder on the insulating material aroundsaid center electrode.

24. In combination, a spark plug shell, a gland nut internally engagedwith said shell, a bushing of material having good thermal conductivityin said nut, an insulating cigarette disposed in said bushing, a centerelectrode mounted in said cigarette, a portion of said electrodeextending inwardly from the outer end of said nut being of greaterthermal conductivity than a portion next outwardly thereof, insulatingmaterial around said center electrode substantially coterminous withsaid portion next outwardly of said nut, said material being providedwith an outwardly 'facing shoulder, means associated with the outer endof said electrode to increase the thermal conductivity thereof, anexternally threaded member having good thermal conductivity disposedaround and secured to the outer end of said electrode, a sleeve ofinsulating material cooperating with the shoulder on said insulatingmaterial around the center electrode to form a seal at that point andextending outwardly beyond the end of said electrode, a heat conductingelement engaged with said externally threaded member and in heattransferring relation with said sleeve, a cylindrical element disposedin said sleeve and extending beyond the outer end thereof, a sealingelement around said cylindrical element in contact with the outer end ofsaid sleeve, laterally apertured radio-shielding means disposed aroundthe outer end of said electrode, an element of a shielding harness foran ignition cable, and means to secure said last named element incooperative relation With said radio-shielding means and to maintain aneffective seal at said sealing element and at the shoulder on theinsulating material around said center electrode.

' 25. A shield for spark plugs, comprising a metal member disposablearound the outer portion of the plug, said member having a portionelectrically connectible to the grounded shell of a spark plug, aportion ,electrically connectible to the shielding harness of anignition cable, and an intervening portion comprising longitudinallyextending spaced apart Abars, the said bars being formed ofmaterialhaving low thermal conductivity and the width of each bar not exceedingthe diameter of the spark plug.

26. A shield for spark plugs, comprising a metal member disposablearoundthe outer portion of the plug, said member having a-portion electrcallyconnectible to the grounded shell of a' radio shielding member inelectrically conducting 3 relation with the base of said plug, saidmember' being circumferentially discontinuous over a por.. tion only ofits length, and elements associated with the outer end of said membercoacting with the outer end of said plug to form a moisture proofenclosure for the outer terminal of the plug and the ignition circuitparts contacting said terminal.

MELVILLE F. PETERS. ALLEN V. ASTIN.

